Electrical testing apparatus



Mary l5, 1951 A. H. LAMB 2,552,981

ELECTRICAL TESTING APPARATUS 'Filed-Feb. 1:5; 1947 3 sneetssheet 1 m QWQWV'M,

May @195g A. H. LAM@ 2552.9@

ELECTRICAL TESTING APPARATUS Filed Feb. 13, 1947 S''Shts-Snefefe 3 A }.//Jr an/es/lfar :Pa dll/loer sars auf ,Pes/:Sfar Ea le/fer Patented May l5, 1951 ELECTRICAL TESTING .APPARATUS Anthony H. Lamb, Hillside, N. J., assignor to Weston Electrical Instrument Corporation, Newark, N. J., a corporation of New Jersey Application February 13, 1947, Serial No. 728,315

13 Claims.

This invention relates to electrical testing apparatus and more particularly to portable apparatus for checking the continuity and/ or measuring the voltage, current or resistance of an electrical circuit.

A conventional type of portable testing apparatus includes a measuring instrument and one or more dry cells within a casing which is placed on a shelf, table or other support, and a pair of leads terminating in test prods for engagement with points on the circuit under examination. It is usually impossible to place the portable casing in such position that both the instrument and the 'circuit under test can be viewed at the same time, and the checking of the circuit then requires considerable time as the operator must turn his head back and forth continuously to set the prods and to take the readings. Damage occurs frequently as the casing may be pulled from its support o1' the prods may slip, when the operator turns to take a reading, and create a short circuit or impose an excessive voltage upon the instrument.

Objects of the present invention are to provide electrical testing apparatus which eliminates the separate instrument casing of the prior constructions, and in which all of the electrical elements areY located on or within the insulating handles of the test prods. Objects are to provide electrical testing apparatus of small size and highly portable character which may be readily adjusted to test or measure various electrical factors such as circuit continuity, voltage, current or resistance. More specifically, an object is to provide electrical testing apparatus in which a miniature measuring instrument is mounted within the handle of one of the test prods and other circuit elements, such as dry cells, resistances and/or rectiers, may be located in the same or in the other handle in any desired combination in accordance with the particular test or measurement which is to be made. Further objects are to 4provide electrical testing apparatus in which various circuit elements are interchangeably received in the handles of the test prods, and any one of a number of circuit connections may be established to adapt the measuring instrument for diierent types of tests and/ or different ranges of measurement.

These and other objects and advantages of the invention will be apparent from the following specification when taken with the accompanying drawings in which:

Fig. 1 is an .elevation of an electrical testing apparatus embodying the'invention;

Fig. 2 is a fragmentary elevation with parts. in section, showing a test prod in reversed or inoperative position;

Figs. 2a and 2b are elevations of other types of circuit elements which may be placed in the test yprod handle or handles;

Fig. 3 is an elevation of another embodiment of the invention;

Fig. 4 is a substantially longitudinal section, on a larger scale, of the hollow handle and the measuring circuit elements housed within the same.

Fig. 5 is a top View of the mounting washer by which the instrument is supported within the handle;

Fig. 6 is a bottom view of the instrument assembly as seen on the sectional plane indicated by line 6 6 of Fig. 4;

Fig. 7 is a fragmentary sectional view, also on an enlarged scale, of another embodiment in which the measuring instrument scale extends across the end of one of the test prod handles;

Fig. V8 is an end elevation of the test prod handle and measuring instrument within the same;

Fig. 9 is an elevation, partly in longitudinal section, of a multi-range embodiment of the invention; and y Fig. l0 is a schematicview of a multi-purpose measuring instrument embodying the invention.

In Figs. 1 and 2 of the drawings, the reference numeral I identies the cylindrical casing of a handle which is closed at its lower end by a metal plug 2 having a central bore in which the test prod 3 is threaded. The casing is of insulating material, and preferably a transparent plastic, and the metal plug 2 is set back from the end of the casing I to prevent an inadvertent electrical contact between the plug 2 and a circuit element other than that engaged by the test prod 3. The prod 3 has cylindrical knurled portions 4 at opposite sides of, and of somewhat smaller diameter than the threaded portion 5, to facilitate the reversal of the prod 3, as shown in Fig. 2, to prevent damage to or from the sharp point of the prod 3 during transportation of the test apparatus. As shown in Fig. 2, the relatively long pointed end of the prod 3 lies Within the skeleton extension 2' of the metal plug 2 when in reversed position.

A miniature electrical measuring instrument I, preferably of the general type described and claimed in my copending application Serial'No. 584,759, filed March 26, 1945, is supported within the upper end of the casing I. Measuring instruments of high sensitivity may be manufactured in small sizes, for example of a diameter to fit within a casing I having an outside diameter oi l inch, according to my prior invention, and the instrument scale may be graduated in one or more of the electrical quantities of current, voltage and resistance. The instrument I is secured to and below a disk 6 which is threaded into the upper end of the casing I, and one -circuit connection to the instrument is a ilexible lead 'i which extends through a bore in the end cap 3 and is secured to the disk B'by a screw 9. The other circuit connection is through a spring I which is secured to the instrument assembly and bears upon the extension 2. of the metal plug 2.

The cylindrical casing II of a second prod handle is closed at its lower end by a plug I2 in which a test prod I3 is reversibly mounted in in the manner as described above with respect to the test prod 3. The casing II is of insulating material and may be opaque but preferably, as v illustrated, is transparent.

The. lead I extends through the threaded cap I4..of the casing II, and is secured to the cap I4 by a terminal stud I5. A number of circuit elementsk are supported. within the casing II and electrically connected between the lead terminal I5 and the test prod I3. As shown in Fig. l, one 'circuit element is a dry cell or current source S and another is a resistance R of such value as .to adapt the apparatus for continuity tests and the measurement of resistance values. One terminal of the dry cell S is held in contact with the lead terminal I5 by a spring I which is seated between the lower contact of the resistance R and the skeleton extension I8 of the end cap I2.

' The described apparatus is employed in the customary manner to measure the resistance between the points of an electrical circuit which are engaged by the prods 3 and I3. Both or" the prods may be moved from point to point, or one or the prods may be left at one reference point, `for example the chassis upon which the electrical circuit is mounted. The checking of circuit resistances can proceed rapidly as the prod 3y and the instrument I are continuously in substantially the same line of sight and at approximately the same distance from the operators eyes during the testing. Fatigue and eye strain are reduced to a minimum in the case of tests that extend over a long period, which may be the entire work day for an inspector in a factory, as the close association of the instrument I and test prod` 3 eliminates the continuous turning of the head and thealternate focussing of the eyes at different distances which were characteristic of operations with the prior testing apparatus.

The apparatus is small and of light weight, and may conveniently beV carried inthe pocket or in la small case. The prod handles are not unduly large and awkward, but may be of the order of l inch in diameter when the instrument IY is a -fminiature measuring instrument such as described in the copending application.

All of the essential circuit elements of the testing apparatus may be located in the hollow handle of one of the test prods, and the other prod I9 may be mounted in a handle or insulating sleeve 20 which is of but slightly larger diameter than the prod, see Fig. 3. The cylindrical shell 2| of the hollow prod handle is of sumcient length to receive an instrument I and such other electrical elements, for example a resistor R, and dry cell S, as may be-required to adapt the instrument for a particular test orv measurement. .The

lower end of the shell 2l isclosed by a threaded a plug 22 having an outer flange or rim 22y of insu# lating material to prevent an inadvertent shorting of the prod 23 upon some point of the circuit adjacent the particular point engaged by the prod. The plug 22 may be removed to permit the substitution of other components for the cell S and/ or resistor R, and the prod 23 preferably has milled cylindrical portions 24 at opposite sides of a threaded section 25 to permit a reversal or the prod into inoperative position, see Fig. 4.

A conical spring 26 which maintains a good contactA engagement between adjacent circuit elements has closely wound upper turns threaded upon a bushing 21v which is secured to the insulating base 28 of, the instrument by a stud 29. The soft iron yoke 33 of the instrument I is secured by screws 3l, see Fig. 5, to the metallic washer 3,2, which is threaded into the upper end of the casing 2I and has secured thereto a resilient socket 33 which extends axially through a bore of the insulating end cap 34 of the shell 2 I The pin terminal 35 of the flexible lead from the test prod l5 is plugged into the socket 33 to complete the assembly of. the test apparatus.

The electrical connections to the moving coil 36 of the instrument I- include the springs 31, 38 which are anchored, respectively, on the yoke 3i] and on the strap or bracket 39 which is clamped between the bushing 27 and the insulating base 28. The core 46 of the instrument is a permanent magnet and the angular displacement of the coil 36, and of its pointer 4l with respect to a scale plate 42, depends upon the magnitude of the current through the coil 36.

There is a denite limit to the maximum current which may pass through the instrument I, but the measuring range of the testing apparatus and the type of test or. measurement may be varied by a selection of thev values and the character of the circuit elements which are located in the test prodv handle or handles. As illustrated in Figs. 1, 3 and 4, a resistor R and dry cell S are connected in series with the instrumentv I, andthese embodiments of the invention are adapted for continuity tests and for the measurement ofresistance values. The illustrated-instrument-scale plates are provided with graduations of microamperes and of ohms, and the testing apparatus may be converted to measure direct current values, in place of resistance values, by removing the dry cell S and substituting a simple connector unit of substantially the same length. Alternatively, the apparatusmay be employed for alternating current measurements by removing the resistor R and cell S, and substituting a rectifier unit RC, see Figs. 2aand 2b, which includes a crystal rectifier and a resistor ofV appropriate value for the measuringrange indicated by a legend or code marking on the cartridge.

Asl shown in Figs, 7 and 8, an instrument I may be employed which has a pointer 4I movable'over va scale plate 42'V arranged in a plane transverse to the axisof the cylindrical probe handle 44. The instrument is mounted upon an Iinsulating disk 45 which is threaded into the end of the casing, and the outer end of the casing is..closed by a transparent cap 46. on the end of a sleeve 41 which has a snug nt upon the re- .duced diameter upper portion of the disk 45. `One spring or instrument coil terminal is connected by a strap 48 to the spring 49 which is attached to the disk 45 and bears on a cartridge lorcircuit element; 5B of a desired character, and the other spring .or coil terminal connectedtol a strap 5l which is mounted on the disk 45 and has a lower end in line with an opening 52 {through the casing wall in which may be nserted the pin terminal of a flexible lead, not shown.

Other embodiments of the invention, as shown in Figs. 9 and 10, include a plurality o f pin sockets in which terminal pins of leads may be inserted in various combinations to permit multiple-range or multiple-purpose measurements without change of the circuit elements located within a handle of a rtest prod. The apparatus shown in Fig. 9 may be used for measurements of the same type in four ranges, and the apparatus shown in Fig. 10 provides for measurements of different type, and measurements of one type in different ranges.

In the embodiment illustrated in Fig. 9, the instrument I may be substantially identical with the instrument which is shown in Fig. 4, and it is secured to an insulating disk 53 which is threaded into the upper end of the transparent plastic casing 54 of a probe handle. The lower end of the casing is closed by a threaded plug 55 in which a probe 56 is mounted; these parts being preferably similar to the corresponding parts of the previously described embodiments of the invention. Two resistors Ra, Rb, preferably of different values, are serially arranged between the skeleton extension 5l of the end plug 55 and a spring 58 which is secured to` the insulating base disk 59 of instrument I and conductively connected to one terminal of the instrument I by a strap 60. The other terminal of the instrument has a spring contact 6I secured thereto for engagement with the lower end of a resilient socket S2 in an end cap 53 which is threaded into the end of the casing 54. A lead 54 extends from the terminal strap 60 to a spring contact 55 which is mounted on the disk 53 to engage a resilient socket 6E carried by the end cap 63. The resistors Ra, Rb are connected through a metal washer or disk 61 from which a flexible lead 58 extends to a contact spring 69 which is mounted on the insulating disk 53 to engage the end of a third Vsocket which is carried by the end cap 63. The lead 68 is of such length that the contact disk 61 may be removed from the casing 53 to permit replacement of the resistor Ra. A flexible lead 'H has a pin 12 at one end for insertion in one of the sockets, and terminates at its other end at the pin or probe contact 'F3 which is carried by an insulating sleeve or handle 14. A jumper or flexible lead 'l5 terminating in pin contacts is provided for altering the measuring range by shunting one of the resistors or alternatively by excluding the other resistor from the measuring circuit.

When the pin contact 'i2 is seated in the socket 62 and the jumper 'd'5 is removed, both resistors are in series with the instrument I to adapt the apparatus for measurements in a high range between the probe contacts 55, and '53. With the pin contacts of the jumper inserted in sockets 65 and lil, as illustrated in Fig. 9, a lower measuring range is provided between probe contacts 55 and 'i3 since the resistance Ra is shunted by the jumper 75. Alternatively, a second low or intermediate measuring range may be obtained between leads 1| and 15 by inserting one pin of lead 'i5 in the socket 10, thereby connecting only the resistor Ra in series with the instrument I between the leads 'H and 75. When the lead l5 is connected to the socket 62, and lead 'H is connected as shown to socket 66, both resistors are excluded from the measuring circuit and. the in-s strument I is directly connected between the leads I I, 'I5 to provide a low measuring range. AAs in the previously described embodiments, one or both of the resistors Ra., Rb may be replaced by the other resistors to shift one or more ofthe higher measuring ranges to other Values.. ,The several circuit combinations which may be established to provide different measuring ranges .are indicated by the legends applied to Fig. 9.v

Additional measuring ranges and/ or additional. types of measurements may be had by increasing. the number and/or types of circuit elements .car-A ried in the handle or handles of the probes, and providing additional sockets into which the leadsl may be inserted. As shown schematically in-Fig. 10, the measuring instrument I is located in the` upper end of the cylindrical probe handle- 'I6-inv the manner illustrated in Fig. 7, and the circuit elements within the handle include two resistors Ra, Rb, a crystal rectifier C, and a dry cell or current source S. One terminal of the instrument I is connected to the probe il by a lead- T3, and the other instrument terminal is con-l nected to a pin socket E53 by a lead 8G. Thesocket. is also connected to one end of each resistor Rag. Rb and of the rectifier C by a common Ylead 8|, and the other ends of these circuit elements are connected by individual leads 82, 83- and Srl-to pin sockets 85, 86 and 87, respectively. The dry cell S is connected between a pin socket 88 and the lead 83 of pin socket 85 85 by leads 89, Sil, respectively. The circuit connections within the probe handle may be established in any convenient or desired manner which permits the removal and replacement of any of the circuit elements;` for example by coupling washers and flexible leads such as illustrated in Fig.` 9, or the cylindrical case 15 may be made in two or more sections to facilitate replacement of the circuit ele-- ments.

The instrument I may be connected across points in a circuit under test by inserting the pin. end of a test prod lead in the pin socket 19, and

" contacting the circuit points with they test prod and the probe Ti. 'I'his connection and the several measurements which may be made when the test prod is connected to other pin sockets are indicated by the legends applied to Fig. 10.

Embodiments of the invention are of exceedingly small size and bulk, as compared with prior portable apparatus for making the same tests or measurements, since the test prod handles are comparable in size to the so-called pencil nashlights, i. e. they may have a length of only a few inches and a diameter of one inch or less. A minimum size is possible when the measuring instrument and all circuit elements are located in a single probe handle, but the invention is not limited to constructions of the minimum size consistent with stability in use and economy in manufacture. It may be desirable to employ measuring instruments of substantially more than minimumsize when the testing apparatus is to be used continuously for long periods. The longer scale plate of a larger instrument will reduce eye strain for such uses, for example when the testing apparatus is used throughout the work day by an inspector in a factory manufacturing radio or television apparatus. I

It is therefore to be understood that the invention is not restricted tothe apparatus herein l illustrated and described asvarious changes may in t'lcl'e.-c'lsiaracterl .of the circuit. elementswlithout departingv from-thespirit andrscopebf: thev miren; tion as .setiorth in thetollowing claims.

g 1. Electrical testing apparatus; comprising a hollow prod handle, a mounting-mate, renier/abit disposed .wi-thinsaid handleat one end ztheree, electrical measuring instnument of the. nerr-na.: nent magnet .corefmouabla coil. .type .depending from said mounting plate, said. instrument.im.- cluding a subbase or insulating material, a lcoiled spring carriedby. and depending :fromwsaid sube base, an` electrical connection .between :the ,upper end o f; Asaid spring and one side .of said instiue ment coil, circuit elementremorahly .disposed withinsaidh ndleand engageable ith@ lower end of sai spring, a removable and closure for the `other fend. of said, handle. anrod carried in said closure member, the rested arrangement .bgins such that when Saidclosure member :is tackled t said handle a series electrical Circuit... established.. from ,Said coilend throuehsaid sp ne and. Cruit; element to Said. pred and electrical connecting means irmludingv a @crible lead @X- tendine from the other Side of .Said instrument coil toasecond prod.

.2- Testine apparatus as `d elies in daim .1 wherein Said end closure member ,has .a threaded, bore and said iirst test prod has a blunt end and a 1,noiilllnd connected by a threaded Dertien en: Saeeable insaid bore whereby Saidnrod may-'ee rev-H5915. flanged t0 Drole@ either its DQH @Qd or blunt end.

V3o. Electrical testing apparatus as defined in claim 1 wherein the end ofv said fleitiblellead-,oppositetlie yprod end terminates ontaictpin and s .aid prod handle includes a cooperative pin socket electrically connected to the said other-side of the instrument coil.

4. Electrical testing apparatus .as defined in claim 3 wherein saidl socket Yis Acarried by said mounting plate. Y

,5. Electrical testing apparatus as donned in claim 1 wherein said mounting plate is of insulating materialand said connecting means includesa Contact pinat the nead of {s aidiiexitble lead .opposite said second prod, la pin socket cooperative with said pin, and a contactterminal on said mounting plate electrically connected to said socket and to said other side of -said instrument coil.

'6.'Electrical testing apparatus as dened in claim 1 and which further includes a second circuit element in said hollow prod handle connected inseries vwith the first said circuit element, one of said circuit elements being a dry cell battery and the other a resistor adapting said testingy apparatus for use asian ohmmeter.

7. Electrical testing apparatus as dened in claim 1 wherein said circuit element is constituted by a cartridge containing a rectifier unit adaptingsaid apparatus for measurement of alternating 'current voltages.

8. Electrical testing apparatus asdeiined in claim 1 wherein 'said circuit element is constituted by a cartridge including series connected rectifier and resistor unitsadapting said apparatus for measurement of alternating current voltages.

A9. vElectrical testing apparatus comprising a pair of prods to be appliedl manuallvto points of--acircuit to be tested-handles for' said prods, at'least one of said handlesbeing1a-hollow cylf inder' 'threaded. internally= at one end *thereon a mounting plate-screwed into the threadedendbf said `italien handle; an .electrical measurme strugnentysupnorted Within. .said hQllQW, Ilaria-1? byL said mounting plate, said instrument Dgllnf the permanent Vmagnet corefmQi/able C Ql time., El' cap member screwed into the threaded end ,Qisaid hollow handle, .a pin socket inA said can member, connections between-said socket and one, end of said-` instrument coil, a `detachable. .closure mem: benat the other .end of said hollow handle hav..- ing .one ofv said prods secured thereto, rcircuit elements connecting the .other end vof said in,- strumentcoilwith 4the prod secured to said closurememher, and a flexible lead having at one end thereof. a pin terminal insertable .in said socket, the otherendofsaid lead being ,electrically connected 'with said other prod.

10. Electrical testing apparatuscomprising ,a hollow prod handle, a Amountingv plate Vof insulatingmaterial ,removably disposed within said. handleat one end thereof, an electrical measuring instrument of 4.the permanent magnetcore-mow able coil .type depending from said mounting plate, said instrument including a sub-base of insulatingrfmaterial, a,.coiled spring carried by and.depending from .said sub-base, an electrical connection .between the tupper end ofsaid spring andone sideofsaidlinstrument coil, aremovable end closure .for the other end of said handle, va prodcarried-by .said yclosure -memben la pair of circuit elements removably disposed within said handle, said .elements being series connected between the lower end of 4saidspring andsaid-prod whensaid closure Jmember is attached -to said handle, a nsecond .prod Vterminati-ng one -end -of a exiblefleada contact pin terminatingthe opposite end of saidlead, alpin socket cooperative with-saidpin, a contact terminal on said mounting plate electrically connected to said socket and .to the othervside-of said instrument coil, a second :pin socketelectrically connectedwith a second Acontact terminal on saidvmounting plate, electrical connecting means'extending between said .second contact `terminal and a point intermediate -said l pair of I circuit elements, a v third pin socket `electrically connected With a third contact Iterr-ninal onfsaid mounting plate, elctricalconnectingmeans extending lbetween said third-*contactterminal and the side of saidfihnstrument coilv connected to said spring, and A a second-flexible lead having contact lpins zatthe terminal ends thereof cooperative with said second and third pin sockets.

ll .-Electrical testing apparatus comprising a pairoofzprodstobe applied manuallyto points of 4a circnitgtobe tested, handles for saidprods, at-ieastpneof saifihanuies ,being hollow and cylindricallwith itsV associated prod vprojecting axially from one end thereof, a.remlovable closure .member for the vprod end ,of saidf'hollow handle and which carries said prod, an-electrical measuring instrument supportedwithin saidfhollowhandle at the other fend thereof, said instrument being of the permanent magnet coremovablecoil type, and circuit elements connecting said instrument coil in serieswith said prods, one of said circuit elements being la flexible Ylead extending between said handles, and another of saidl circuit elements being a coiled contactspling secured to said instrument and extending axially from oneend thereof with one. end of said spring beingielectrically .connected to one side off. said instrument coil.

.12. Electrical testing apparatusas .deined` in vclaim'A 11 wherein said ekibleleadincludesapin contact at one end thereof engageable in a pin socket carried by said hollow handle at the instrument end and electrically connected to the other side of said instrument coil.

13. Electrical testing apparatus comprising a hollow prod handle of cylindrical shell form, a v

lower end closure for said handle carrying a test prod, an electrical measuring instrument including a cylindrical permanent magnet core and a movable coil coaxial with said core, means supporting said instrument within and at the upper end of said prod handle, a plurality of pin sockets on said prod handle selectively connected to said plurality of circuit elements, a flexible lead terminating in a cooperating prod, and a pin terminal at one end of said lead insertable in a desired one of said sockets to include one or more of said circuit elements in series circuit with the coil of said measuring instrument.

ANTHONY H. LAMB.

REFERENCES CITED The following references are of record in the ille of this ipatent:

UNITED STATES PATENTS Number Name Date 1,528,709 Trimble Mar. 3, 1925 1,593,024 Macadie July 20, 1926 1,606,063 Edwards Nov. 9, 1926 1,615,788 Feldkamp Jan. 25, 1927 1,707,051 Colosoi Mar. 26, 1929 1,888,906 Coloso Nov. 22, 1932 1,957,802 Rabezzana May 8, 1934 2,156,319 Steele May 2, 1939 2,231,660 Carlotti et al. Feb. 11, 1941 2,290,760 Mehafle July 21, 1942 2,413,521 Roskilly Dec. 31, 1946 2,418,872 Fisher Apr. 15, 1947 OTHER REFERENCES Electrical Review, Feb. 5, 1926. Radio and Television. Feb. 1940. Popular Mechanics, Sept. 1944. Electrical World. August 8. 1925. 

